Capacity control for reciprocating compressors



Jan. 20, 1953 c. M. ASHLEY 2,625,099

CAPACITY CONTROL FOR RECIPROCATING COMPRESSORS Filed Aug. 22, 1946 4 Sheets-Sheet 1 FIG. I

I I I I I I I I l I I I I I I I I l BY 222R.

Jan. 20, 1953 4 Sheets-Sheet 2 Filed Aug. 22, 1946 FIG.2

INVENTOR.

Jan. 20, 1953 c. M. ASHLEY 2,626,099

CAPACITY CONTROL FOR RECIPROCATING COMPRESSORS Filed Aug. 22, 1946 4 Sheets-Sheet 5 I a as 42 32 I0 I 47 4s- 40 will a? A IN V EN TOR.

BY- g Jan. 20, 1953 c. M. ASHLEY 2,626,099

CAPACITY CONTROL FOR RECIPROCATING COMPRESSORS Filed Aug. 22, 1946 C 4 Sheets-Sheet 4 IN V EN TOR.

Patented Jan. 20, 1953 CAPACITY CONTROL FOR RECIPROCATING I COMPRESSORS Carlyle M. Ashley, Fayetteville, N. Y., assignor to Carrier Corporation, Syracuse, N. Y., a corporation of Delaware Application August 22, 1946, Serial No. 692,326

In Argentina September 22, 1947 I 14 Claims.

This invention relates to reciprocating compressors and more particularly to a system of capacity control for reciprocating compressors.

The chief object of the present invention is to provide a system of capacity control for reciprocating compressors which permits the capacity of a compressor to be adjusted in response to load conditions and which is so designed as to prevent rapid recycling during operation of the compressor.

An object of the invention is to provide a system of capacity control for a reciprocating compressor having a plurality of cylinders which permits complete cylinder unloading by fixed steps to reduce the capacity of the compressor.

A further object is to provide a system of capacity control for a reciprocating compressor in which the compressor cylinders may be unloaded in sequence by holding the suction valve of each cylinder open thereby permitting easy and ready starting of the compressor, permitting the use of normal torque motors for driving the compressor, and enabling variation in the capacity of the cylinder in response to changes in load conditions.

A still further object is to provide a capacity control for a reciprocating compressor in which cylinder unloading is accomplished in response to a change in suction pressure and in which the control may be adjusted or reset in response to variation in room temperature, if desired, to maintain a constant cooler water temperature, a constant relative humidity or dewpoint of conditioned air or the like. Other objects of my invention will be readily perceived from the following description.

This invention relates to a system of capacity control for reciprocating compressors which comprises oil pressure actuated elements for holding compressor valves in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to the elements and means responsive to load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the supply of oil to the elements in sequence in accordance with load conditions.

The attached drawing illustrates a preferred embodimentof my invention in which:

Figure l is a diagrammatic view illustrating a compressor including the capacity control of the present invention;

Figure 2 is a sectional view illustrating the position of the capacity control within the crank caseof the compressor;

Figure 3 is a view partly in elevation and partly in section illustrating means for disposing the suction valve of a cylinder in inoperative position;

Figure 4 is a sectional view of the control valve; and

Figure 5 is a sectional view of the regulating valve.

Referring to the attached drawings, there is illustrated in Figure 1 a compressor 2 having a plurality of cylinders 3, 4, 5 and 6. The compressor may be of any conventional design and includes a crank case I, the bottom of which serves as an oil sump 8; the operating mechanism includes the usual crank shaft 9, pistons I0, connecting rods I I and other structural elements normally employed in compressing gas, all of which form no essential part of the invention, but which it will be understood are present to form an operable compressor.

It will be appreciated in various applications to which a compressor may be applied there is a need for varying the output responsive to differing or changing load requirements. For this purpose there may be provided suitable unloading mechanism designated generally at I2 adapted to hold the suction valve I3 of a cylinder in inoperable position. Unloading mechanism I2 may be actuated by means of a power element I4 actuated by oil pressure. It will be appreciated mechanism I2 and elements I4 may be provided for any desired number of cylinders of a compressor.

A pump I5 is provided for pressure lubrication of moving parts of the compressor. A control valve I6 is connected to pump I5 by a line H. A

relief valve I1 is disposed in line H to maintain a constant oil pressure to the moving parts of the compressor and to control valve I6. Control valve I6 is connected to the various power elements I4 by means of lines I8. Control valve I6 serves to permit or to discontinue the supply of oil to each power element I8 in sequence, that is, one after the other as hereinafter described. A regulating valve I9 is connected to control valve I6 by means of line 20 and serves to regulate or adjust control valve I6 as hereinafter described. Regulating valve I9 is connected to the sfiaiioii manifold of the compressor by a line 2 I; oil may be drained from valve I9 to sump B through line 22.

The general arrangement of the capacity control is illustrated in Figure 2. The capacity control preferably is disposed in the pump end cover 23 of compressor 2 and oil is supplied thereto by pump I5 through line I! to a filter 24. From filter 24 it passes through line 25 to control valve I6.

Oil may be supplied from control valve I6 through lines I8 to the various power elements I4. Valve I6 is connected to valve I9 by line 26. A T 26 is disposed in line 26 and permits passage of oil throughline 2'! to a suitable gauge 26 adapted to register control oil pressure for the information of the operator.

In Figure 3 there is illustrated suitable mechanism I2 used for disposing the suction valve of a compressor cylinder in inoperative position. It will be appreciated similar mechanism may be provided for each cylinder of the compressor if desired. Mechanism I2 employed toplace suction valve I3 in inoperative position consists of lifter sleeve 29, lifter pins 30, loading springs 3| and a retainer ring 32. Preferably, such -mecha nism comprises a self-contained sub-assembly with the removable cylinder sleeve 35 in which the compressor piston I6- operates. Suction gas from themanifold 34 enters the suction valve port 35 and passes through such port into the interior of the compressor cylinder when valve I3 is moved away fromthe port 35. When pins 39 are in the position illustrated in Figure 3, the suction valve I3:closes at the end of each suction stroke under the urging of suction valve springs 36. After com pression of the gas in the cylinder, the gas is discharged through discharge valve 31 into the cylinder head space 38. Pins 36 remain retracted while full oil pressure is applied to power element I4 and aremoved upward to hold valve I3 in inoperative position when oil pressure on element I4 is discontinued, as hereinafter described.

Powerelement I4 consists of a casing 39 havinga base 40 and'a top cover 4|. A piston 42 is disposed in casing 39 and is connected by a rod 43-to a forked lever 44 operating on a fulcrum 45 disposed at one end of cover M. The lever 44 terminates in portions 46 adapted to engage the lif ter sleeve 29 surrounding the cylinder. A piston springv 41 applies a predetermined pressure to piston 42; in the absence of oil pressure supplied to element I4, piston 42 rests against the bottom cover 40. A vent 49 may be provided in power element I4 to permit oil which seeps past piston 42 to returnto the crank case I of compressor 2. Preferably, the power elements I4 are located in the suction manifold of the compressor adjacent the cylinder to be unloaded.

When oil pressure is supplied to power element I4, piston 42 moves upward, permitting lever 44 to pivot about fulcrum 45 thus permitting sleeve 29 to be u-rgeddownward by springs 3| until such movement is halted by contact of sleeve 29 against ring32. Downward movement of sleeve 29 carries pins 60 therewith thus permitting suction valve I3 to-be disposed in operative position; When pressure is removed from power element I4 as by, forexample, discontinuing 'the'passage of oil thereto, .piston 42 is forced downward by spring 41, pivoting lever 44 about fulcrum 45 and urging sleeve29'in an upward direction to raise pins 39, thus holding valve I3 away from port 35. With the suction valve disposed in an open position, no compression of gas takes place in the cylinder and the capacity of the cylinder is zero.

In Figure 4 I have illustrated the control valve I6. Control valve I6 is an oil pressure actuated, multiple port, snap action piston valve. Oil pressure is supplied to a chamber 49 of valve I6 through line 25. A piston 50 is disposed in chamber 49. Piston 50 is provided with a plurality of grooves for a purpose hereinafter described. A spring 52 is held in chamber 49 by a cap 53 and provides a. predetermined pressure to urge piston 56 longitudinally of the chamber. The end 54 of piston 50 serves in efiect as a partition separating or dividing chamber 49 from a second chamber 55. An opening 56 in end 54 connects chambers 49 and 55. Chamber is connected to regulating valve I9 by line 29.

A plurality of outlets 5? is provided in chamber 49 and are adapted to be connected to lines I8 respectively leading to the various power elements I4. An opening 58 is drilled in the wall or casing of valve I6. A spring 59 is disposed in opening 58 and serves to urge a ball member 60 Within one of the grooves 5I in piston 55. Ball member 60 may be loaded with any requisite pressure by means of spring 59.

Regulatingyalve I 9 is shown in Figure 5. Valve I9 includes achamber 6| in which is disposed a bellows 62. Bellows 62 is subjected on one side to suction pressure through inlet 65. On its opposite side, bellows 62 is subjected to a predetermined force exerted by range adjustment spring 64. The force'eXerted by spring 64 -may be adjusted by means of stem 65 carrying a traveling nut 66. In addition, such side of the bellows is subject to atmospheric pressure.

A port 61 is provided in valve I9 adapted to be closed by a valve member such as a needle 68. A plurality of push rods 69 are provided which convey movement of bellows 62 to member 68. Oil is admitted to the valve through inlet lilfrom line 26 connecting the valve with chamber 55 of valve I6. When port 61 is opened by movement of member 68 therefrom, oil is free toflow through the port and through outlet 'II to the crank case of the compressor. An'auxiliary spring 12 is provided which operates in opposition to adjustment spring 64 to permit operation in the vacuum range of suction pressure and to lock out the control valve when spring 64 isat its free height.

It will be appreciated the loading imposed on spring 64 may be adjusted to vary the suction pressure at which member 68 tends to move from port 61 to open the valve to the passage of oil. Opening I3is drilled through the Wall of valve I9, such opening being closed by plug 14; Suitable means may be attached to valve I9 through such opening if desired to vary pressure on the outside of the bellows thus varying the loading imposed upon the compressor so that the setting of the control valve may be varied in response to dewpoint temperature, cooler water temperature, room temperature or the like.

In normal operation oilfrom the lubrication systempump I5 enters the pump end cover 23 through removable filter or strainer 24 as shown in Figure 2. From thestrainer 24, oil passes through line 25 to the inlet connection of valve I6. Depending upon the position of piston 56 in chamber 49 certain of theoutlets 57 are supplied with oil at full pressure, such oi1 being conducted by lines I8 to the various power elements I4. Oil in chamber 49 passes through opening 55 into chamber 55 in valve I 6. Chamber 55 is connected by means of line 26 to regulating valve I9. If the valve port 61 invalve I9'is open, valve member 68 being moved away from the valve seal, oil is free to pass through port 61 into the crank case through outlet II in the wall of valve I9.

Assuming port 61 is open, its efiective area is approximately three times as great as the area of the opening 55. Whenport 6? is open the oil pressure in chamber 55 is reduced to approximately 10% of full oil pressure. When valve member 68 moves to restrict valve port 61 in response to changes in load conditions reflected by a change in suction pressure, oil pressure in chamber 55 increases; when port 6'! is closed completely, oil pressure in chamber 55 increases to the full supply pressure from the lubrication system. As the contro1 oil pressure in chamber 55 varies in response to the movement of valve member 68 in regulating valve l9, piston 50 moves abruptly to open or to close outlets 5'! in sequence. The application or removal of oil pressure to the various power elements I4 operates the unloading mechanism l2 to unload or to load the various compressor cylinders.

As an example, assume the compressor is operating at 40 pounds per square inch suction pressure; the range adjustment spring 64 has been previously adjusted so that the moving parts of regulating valve l9 are in equilibrium, with port 51 closed by valve member 68. Under such circumstances, oil pressure in chamber 55 is full supply pressure and piston 50 is at one end of its stroke with all outlets 51 supplied with full oil pressure. The pins 30 of unloading mechanism I2 are retracted and suction valve operation is normal with compressor capacity at its maximum. If the refrigeration load be reduced, the suction pressure tends to decrease permitting valve member 68 to move away from port 61 permitting passage of oil therethrough and decreasing the oil pressure maintained in chamber 55. At an oil pressure value determined by the loadings employed on spring 52 and spring 58 piston 50 will move abruptly to vent one outlet 57 to the crank case 7. Discontinuing oil pressure to one power element operates the unloading mechanism to dispose the suction valve in inoperative position thereby unloading one compressor cylinder. Suction pressure as a-result increases to find a new equilibrium condition with the reduced refrigeration load. A further reduction in refrigeration load will again reduce the suction pressure to cause valve member 68 to move a greater distance from port 61 permitting increased flow of oil through the port to the crank case and a further reduction of oil pressure in chamber 55 with a result that piston 55 again moves abruptly to vent a second outlet 51 to the crank case with the result that a second cylinder is unloaded. Additional cylinders are unloaded in sequence, depending upon load conditions. An increase in refrigeration load reverses such operations. The capacity control system provided by the present invention in effect tends to hold the suction pressure substantially constant for wide variations of refrigeration load.

By complete cylinder unloading, capacity reduction isobtained in fixed steps; for example, on a four cylinder compressor, three cylinders may be equipped with the control and the steps of unloading may be 75%, 50% and 25% of full capacity. Such steps, of course, are unequal in relationship to each other since, for example, assuming the compressor has two cylinders unloaded and is balancing itself against a refrigeration load, the unloading of a third cylinder means a 50% reduction in capacity. Refrigeration load changes are gradual and do not match the abrupt increments of compressor capacity. As a result, the suction pressure rises after each reduction in compressor capacity. Unless the pressure differential between the loading and unloading points of each cylinder is great, cyclic operation of the system will occur at intermediate loads. It is normally desirable to hold the suction pressure substantially constant with refrigeration load variation and accordingly it is desirable that 6 cyclicunloader operation occur. i Such operation, however, should not occur rapidly. The present invention prevents rapid cycling at lighter loads despite the increasing magnitude of each step of capacity in relation to the previous step.

Excessive cycling is eliminated in the present system since the control is actuatedby a controlled oil pressureobtained by use of a fixed upstream orifice and a regulating valve port and valve member of specific characteristics. In addition, the provision of a control valve actuated by oil pressure permits the snap action ball memberto be loade-din such-manner that the pressure differential between loading and unloading of any cylinder is largein relationship to-thepressure differential betweenloading or unloading points of successive cylinders; Such" practice maintains the over-all system differential small without causing rapidcycling. i r

If desired, refer to Figure 5, compensated control of compressor capacity may be applied to the system described above to permit automatic resetting ofthe valve to maintain constant cooler water temperature, constant relative humidity or dew-point of the air or the like. A temperature actuated pneumatic control responsive to room temperature may be connected to valve I9 through opening l3. by the removal of plug 14 thereby varying or changing the pressure imposed upon bellows 62 in accordance with variation in room temperature. Likewise,if desired, an electrical control system may be used to provide compensated control ofcompressor capacity in place of the pneumatic system described. For this purpose, a control motor equipped with a suitable cam may be mounted on the apparatus so that the cam operates the adjustment stem 55. Operation of the motor in turn may be controlled by any suitable means responsive to room temperature.

The present invention provides accurate control of compressor capacity in response to load conditions. The control system is so designed as to permit ready adjustment thereof merely by employing springs with difierent characteristics. An advantage of the present invention resides in the fact that the control arrangement may be readily changed or varied Without necessitating tearing down the compressor. The entire suction pressure range of operation of the compressor may be readily adjusted by adjusting or changinga simple adjustment spring in the regulating valve. The oil actuated means of the present invention decrease the amount of cycling of the unloading mechanism thus reducing wear on the suction valve and the unloading mechanism while improving the operation of the refrigeration sys- While I have described and illustrated apreferred embodiment of my invention, it will be understood my invention is not limited thereto since it may be otherwise embodied Within the scope of the following claims.

I claim:

1. In a system of capacity control for reciprocating compressors, the combination of an oil pressure actuated element for holding a compressor valve in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to said element, and means responsive to load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the passage of oil to said element in accordance with load conditions.

2. In a system of capacity control for reciprocatingrcompressors, the combination of oil pressureactuated elements for holding compressor valves-in inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to said elements, and means responsiveto load conditions for varying the oil pressure imposed on the pressure actuated means to permit or to discontinue the supply of oil to said elements in sequence in accordance With load conditions.

3. In a system of capacity control for reciprocating compressors, the combination of oil pressure actuated elements for holding compressor valves in-inoperative position, oil pressure actuated means for permitting or discontinuing the passage of oil to said elements, and means responsive to suction pressure for varying the oil pressure imposed on the-pressure actuated means thereby permitting or discontinuing the passage of oil to said elements.

4. Ina system of capacity control for reciprocating compressors, the combination of oil pressure actuatedelementsfor holding compressor valves in inoperative position, an oil pressure actuated valve permitting or discontinuing the passage of oil to said elements, and a second valve responsive to load conditions for varying the oil pressure imposed on the first valve to permit or discontinue the supply of oil in sequence to said elements.

5. In a system of capacity control for reciprocating compressors, the combination of oil pressure actuated elements for holding compressor valves in inoperative position, an oil pressure actuated valve adapted to permit the passage of oil to said elements in sequence, and a second valve responsive to load conditions for varying the oil pressure imposed on said first valve whereby said elements are loaded or unloaded in sequence in response to load conditions.

6. Ina system of capacity control for reciprocating compressors, the combination of oil pressure actuated elements for holding compressor valves in inoperative position, an oil pressure actuated valve permitting or discontinuing the passage of oil to said elements, and a second valve for varying the oil pressure imposed on the first valve, said first valve including a chamber having a plurality of outlets connected with said elements, a piston movable in said chamber, means forrimposinga predetermined pressure on said piston to move it longitudinally in one direction in said chamber, a second chamber having. an opening connecting it with the first chamber, oil flowingv through said opening into the second chamber, said second chamber being connected to the second valve, said second valve having a port therein closed by a valve member, means for moving said valve member toward or from said port in response toload conditions, said first valve including means for yieldably resisting Ion-- gitudinal movement of said piston in said chamber, movement of said piston in said first chamber opening or closing the outlets therein to permit or to prevent passage of oil to the elements, oil pressure building up in said second chamber when passage of oil through said second valve is prevented thereby urging intermittent movement of the piston in an opposite direction against the resistance of the holding means to close the outlets to the elements in sequence in accordance with the load conditions.

7. In a system of capacity control for reciprocating compressors, the combination of oil pressureactuated elements for holding compressor 8 valves in inoperative position, an oil pressure actuated valve permitting or discontinuing the passage of oil to said elements, a second valve responsive to suction pressure for varying the oil pressure imposed on the first valve, said first valve including a chamber adapted to receive oil and having a plurality of outlets therein connected with the elements, a piston movable in said chamber, spring means for imposing a predetermined pressure on said piston to urge it longitudinally in one direction in said chamber, said piston having a plurality of grooves therein, a spring urged ball member disposed within a groove in said piston to resist movement of said piston in said chamber, a second chamber having. an opening connecting it to the first chamber, oil flowing through said opening into the second chamber, said second chamber being connectedto the second valve, said second valve having a port therein closed by a valve member, means in said second valve for moving the valve member toward or from the port in response to suction pressure, movement of said valve member opening or closing the port to the passage of oil therethrough, closing of said port permitting oil pressure to build up in said second chamber, an increase in oil pressure in said second chamber urging intermittent movement of the piston in an opposite direction against the resistance of said ball member thereby closing the outlets in sequence in accordance with the suction pressure.

8. In a step-by-step capacity control for reciprocating compressors, the combination of members for disposing compressor valves in inoperative position, power elements for actuating said members, an oil pressure actuated valve adapted to permit or to discontinue the passage of oil to said power elements, and a second valve responsive to load conditions for varying the oil pressure imposed on the first valve to permit or to discontinue the passage of oil to said elements in sequence.

9. A step-by-step capacity control according to claim 8 in which the first valve includes a chamber adapted to receive oil having a plurality of outlets thereoin connected with the power elements, a piston movable in said chamber, means for imposing a predetermined pressure on said piston to urge it longitudinally in one direction in said chamber, means for yieldably holding the piston against movement in said chamber, a second chamber having an opening connecting it to the first chamber, oil flowing through said opening into the second chamber, the second chamber being connected to the second valve, the second valve having a port therein closed by a valve member, means in said second valve for moving the valve member toward or from the port in response to load conditions, movement of said valve opening or closing the port to the passage of oil therethrough, closing of said port permitting oil pressure to build up in said second chamber, an increase in oil pressure in said second chamber urging intermittent movement of the piston in an opposite direction against the resistance of the holding means thereby closing the outlets in sequence in accordance with load conditions.

10. In combination with a compressor having a plurality of cylinders, a capacity control anplied to at least some of the cylinders, said control including means adapted to hold the suction valves of the cylinders in inoperative position, power elements for actuating said means, said power elements being actuated by oil pressure, a

pump for supplying oil to the compressor, a valve actuated by oil pressure serving to govern the supply of oil to said power elements, and a second valve responsive to load conditions for varying the oil pressure imposed on the first valve.

11. In combination with a compressor having a plurality of cylinders, a capacity control applied to at least some of the cylinders, said control including means for disposing at least some of the cylinder suction valves in inoperative position, power elements for actuating said means, a pump for supplying oil tothe compressor, an oil pressure actuated valve adapted to regulate the passage of oil to said power elements, and a second valve responsive to suction pressure adapted to vary the oil pressure imposed on the first valve, variation of oil pressure on said first valve loading or unloading the power elements in sequence to control the capacity of the compressor.

12. In a system for varying the output of a compressor, the combination of means for loading or unloading the cylinders of the compressor in sequence in response to load conditions, said means comprising members for disposing at least some of the suction valves of the cylinders in inoperative position, power elements for actuating said members, said power elements being actuated by oil pressure, a first valve governing the supply of oil to said power elements, said valve being actuated by oil pressure, and a second valve adapted to vary the oil pressure imposed upon the first valve whereby power elements are loaded or unloaded in sequence in response to load conditions.

13. A system according to claim 12 in which the first valve includes a chamber havin a, plurality of outlets connected with the power elements, a piston movable in said chamber, spring means for imposing a predetermined pressure on the piston to urge it longitudinally in one direction in said valve, said piston having a plurality of grooves therein, a spring urged ball member disposed in one of the grooves in said piston to resist movement of said piston, a second chamber having an opening connecting it to the first chamber, oil flowing through the opening into the second chamber, said second chamber being connected to said second valve, said second valve having a port therein closed by a valve member, means in said second valve responsive to suction pressure for moving the valve member toward or from said port, movement of said valve member opening or closing the port to the passage of oil therethrough, closing of said port permitting oil pressure to build up in said second chamber, an increase in oil pressure in said second chamber urging intermittent movement of the piston in an opposite direction against the resistance of the ball member thereby closing the outlets in sequence to prevent passage of oil to the power elements.

1 1. In a system of capacity control for a reciprocating compressor, the combination of oil pressure actuated elements for holding compressor valves in inoperative position to unload cylinders of the compressor, an oil pressure actuated valve permitting or discontinuin the passage of oil to said elements, and a second valve responsive to load conditions for varying the oil pressure imposed on the first valve to permit or to discontinue the supply of oil in sequence to said elements, said first valve including an oil pressure actuated movable member serving to open or to close outlets to said elements thereby loading or unloading the cylinders of the compressor, and means for yieldably resisting movement of said member, said means being loaded in such manner that the pressure differential between loading and unloading of any cylinder of the compressor is large in relationship to the pressure differential between loading or unloading points of successive cylinders.

CARLYLE M. ASHLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,969,076 Hirsch Aug. 7, 1934 2,032,429 Metzgar Mar. 3, 1936 2,162,570 Bixler June 13, 1939 2,208,428 Nico-let July 16, 1940 2,219,199 Renner Oct. 22, 1940 2,387,117 Buehler 'Oct. 16, 1945 

